Cooling roll, ribbon-shaped magnetic materials, magnetic powders and bonded magnets

ABSTRACT

Disclosed herein is a cooling roll which can provide bonded a magnet having excellent magnetic properties and having excellent reliability. A melt spinning apparatus is provided with a tube  2  having a nozzle  3  at the bottom thereof, a coil  4  for heating the tube and cooling roll  5  having a circumferential surface  53  in which dimple correcting means is provided. A melt spun ribbon  8  is formed by injecting the molten alloy  6  from the nozzle  3  so as to be collided with the circumferential surface  53  of the cooling roll  5  in an inert gas atmosphere (ambient gas) such as helium gas, so that the molten alloy  6  is cooled and then solidified. In this process, dimples to be produced on a roll contact surface of the melt spun ribbon are divided by the dimple correcting means, thereby preventing formation of huge dimples.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a cooling roll, ribbon-shapedmagnetic materials, magnetic powders and bonded magnets. Morespecifically, the present invention relates to a cooling roll, aribbon-shaped magnetic material manufactured by using the cooling roll,a magnetic powder formed from the ribbon-shaped magnetic material and abonded magnet manufactured using the magnetic powder.

[0003] 2. Description of the Prior Art

[0004] Rare-earth magnetic materials formed from alloys containingrare-earth elements have high magnetic properties. Therefore, when theyare used for magnetic materials for motors, for example, the motors canexhibit high performance.

[0005] Such magnetic materials are manufactured by the quenching methodusing a melt spinning apparatus, for example. Hereinbelow, explanationwill be made with regard to the manufacturing method using the meltspinning apparatus.

[0006]FIG. 23 is a sectional side view which shows the situation causedat or around a colliding section of a molten alloy with a cooling rollin the conventional melt spinning apparatus which manufactures aribbon-shaped magnetic material by means of a single roll method.

[0007] As shown in this figure, in the conventional method, a magneticmaterial made of a predetermined alloy composition (hereinafter,referred to as “alloy”) is melt and such a molten alloy 60 is injectedfrom a nozzle (not shown in the drawing) so as to be collided with acircumferential surface 530 of a cooling roll 500 which is rotatingrelative to the nozzle in the direction indicated by the arrow A in FIG.23. The alloy which is collided with the circumferential surface 530 isquenched (cooled) and then solidified, thereby producing a ribbon-shapedalloy in a continuous manner. This ribbon-shaped alloy is called as amelt spun ribbon. Since the melt spun ribbon was quenched in a rapidcooling rate, its microstructure has a structure composed of anamorphous phase or a microcrystalline phase, so that it can exhibitexcellent magnetic properties as it is or by subjecting it to a heattreatment. In this regard, it is to be noted that the dotted line inFIG. 23 indicates a solidification interface 710 of the molten alloy 60.

[0008] The rare-earth elements are liable to oxidize. When they areoxidized, the magnetic properties thereof tend to be lowered. Therefore,normally, the manufacturing of the melt spun ribbon 80 is carried outunder an inert gas atmosphere.

[0009] However, this causes the case that gas enters between thecircumferential surface 530 and the puddle 70 of the molten alloy 60,which results in formation of dimples (depressions) 9 in the rollcontact surface 810 of the melt spun ribbon 80 (that is, the surface ofthe melt spun ribbon which is in contact with the circumferentialsurface 530 of the cooling roll 500). This tendency becomes prominent asthe peripheral velocity of the cooling roll 500 becomes large, and insuch a case the area of the formed dimples becomes also larger.

[0010] In the case where such dimples 9 (especially, huge dimples) areformed, the molten alloy 60 can not sufficiently contact with thecircumferential surface 530 of the cooling roll 500 at the locations ofthe dimples due to the existence of the entered gas, so that the coolingrate is lowered to prevent rapid solidification. As a result, atportions of the melt spun ribbon where such dimples are formed, thecrystal grain size of the alloy becomes coarse, which results in loweredmagnetic properties.

[0011] Magnetic powder obtained by milling such a melt spun ribbonhaving the portions of the lowered magnetic properties has largerdispersion or variation in its magnetic properties. Therefore, bondedmagnets formed from such magnetic powder can have only poor magneticproperties, and corrosion resistance thereof is also low.

SUMMARY OF THE INVENTION

[0012] In view of the above problem involved in the prior art, it is anobject of the present invention to provide a cooling roll which canmanufacture a magnet having excellent magnetic properties andreliability, as well as a ribbon-shaped magnetic material manufacturedusing the cooling roll, a magnetic powder formed from the magneticmaterial and a bonded magnet formed from the magnetic powder

[0013] In order to achieve the above object, the present invention isdirected to a cooling roll for manufacturing a ribbon-shaped magneticmaterial by colliding a molten alloy to a circumferential surface of thecooling roll so as to cool and then solidify it, wherein thecircumferential surface of the cooling roll has dimple correcting meansfor dividing dimples to be produced on a roll contact surface of theribbon-shaped magnetic material which is in contact with thecircumferential surface of the cooling roll.

[0014] According to the above structure, it becomes possible to providea cooling roll which can manufacture magnets having excellent magneticproperties and excellent reliability.

[0015] In this invention, it is preferred that the cooling roll includesa roll base and an outer surface layer provided on an outer peripheralportion of the roll base, and the outer surface layer has said dimplecorrecting means. This arrangement makes it possible to provide magnetshaving especially excellent magnetic properties.

[0016] In this case, it is preferred that the outer surface layer of thecooling roll is formed of a material having a heat conductivity lowerthan the heat conductivity of the structural material of the roll baseat or around a room temperature. This makes it possible to quench themolten alloy of the magnetic material with an appropriate cooling rate,thereby enabling to provide magnets having especially excellent magneticproperties.

[0017] Further, the outer surface layer of the cooling roll ispreferably formed of a ceramics. This also makes it possible to quenchthe molten alloy of the magnetic material with an appropriate coolingrate, thereby enabling to provide magnets having especially excellentmagnetic properties. Further, the durability of the cooling roll is alsoimproved.

[0018] Further, in the present invention, it is preferred that the outersurface layer of the cooling roll is formed of a material having a heatconductivity equal to or less than 80 W·m⁻¹·K⁻¹ at or around a roomtemperature. This also makes it possible to quench the molten alloy ofthe magnetic material with an appropriate cooling rate, so that it ispossible to provide magnets having especially excellent magneticproperties.

[0019] Furthermore, it is also preferred that the outer surface layer ofthe cooling roll is formed of a material having a coefficient of thermalexpansion in the range of 3.5−18[×10⁻⁶K⁻¹] at or around a roomtemperature. According to this, the surface layer is firmly secured tothe base roll of the cooling roll, so that peeling off of the surfacelayer can be effectively prevented,

[0020] In the present invention, it is also preferred that the averagethickness of the outer surface layer of the cooling roll is 0.5 to 50μm. This also makes it possible to quench the molten alloy of themagnetic material with an appropriate cooling rate, so that It ispossible to provide magnets having especially excellent magneticproperties.

[0021] Moreover it is also preferred that the outer surface layer of thecooling roll is manufactured without experience of machining process. Byusing such a cooling roll, the surface roughness Ra of thecircumferential surface of the cooling roll can be made small withoutmachining process such as grinding or polishing.

[0022] In the present Invention, it Is preferred that the dimplecorrecting means includes at least one ridge formed on thecircumferential surface of the cooling roll. This makes It possible todivide dimples to be produced on the roll contact surface effectively,so that it is possible to provide magnets having especially excellentmagnetic properties.

[0023] In this case, it is preferred that the average width of the ridgeis 0.5-95 μm. This makes it possible to divide dimples to be produced onthe roll contact surface more effectively, so that it is possible toprovide magnets having especially excellent magnetic properties.

[0024] Further, it is also preferred that the ridge is provided byforming at least one groove in the circumferential surface of thecooling roll. By forming the ridge in this way, it becomes possible toadjust the width of the ridge and the like accurately.

[0025] Furthermore, it is also preferred that the average width of eachgroove is 0.5-90 μm. This also makes it possible to divide dimples to beproduced on the roll contact surface more effectively, so that it ispossible to provide magnets having especially excellent magneticproperties.

[0026] Furthermore, it is also preferred that the average height of theridge or the average depth of the groove is 0.5-20 μm. This also makesit possible to divide dimples to be produced on the roll contact surfacemore effectively, so that it is possible to provide magnets havingespecially excellent magnetic properties.

[0027] Moreover, it is also preferred that the ridge or groove is formedspirally with respect to the rotation axis of the cooling roll.According to such a structure, it is possible to form the cooling rollwith the grooves and ridges relatively easily. Further, this also makesit possible to divide dimples to be produced on the roll contact surfacemore effectively, so that it is possible to provide magnets havingespecially excellent magnetic properties.

[0028] Moreover, it is also preferred that the at least one ridge orgroove includes a plurality of ridges or grooves which are arranged inparallel with each other through an average pitch of 0.5-10 μm.According to this arrangement of the ridges or grooves, it is possibleto make dispersion or variation in the cooling rates at various portionsof the molten alloy small, so that it is possible to provide magnetshaving especially excellent magnetic properties.

[0029] Further, in the present invention, it is also preferred that theratio of the projected area of the ridge or groove with respect to theprojected area of the circumferential surface is equal to or greaterthan 10%. This makes it possible to quench the molten alloy of themagnetic material with an appropriate cooling rate, so that it ispossible to provide magnets having especially excellent magneticproperties.

[0030] Another aspect of the present invention is directed to aribbon-shaped magnetic material which is manufactured by colliding amolten alloy to a circumferential surface of a cooling roll so as tocool and then solidify it, wherein the circumferential surface of thecooling roll has dimple correcting means f or dividing dimples to beproduced on a roll contact surface of the ribbon-shaped magneticmaterial which is in contact with the circumferential surface of thecooling roll.

[0031] According to the above structure, it is possible to provide aribbon-shaped magnetic material which can provide magnets havingespecially excellent magnetic properties and having excellentreliability.

[0032] In this case, it is preferred that the cooling roll Is providedwith the dimple correcting means described above on the circumferentialsurface thereof. This makes It possible to provide magnets havingespecially excellent magnetic properties.

[0033] In this ribbon-shaped magnetic material it is preferred that aroll contact surface of the ribbon-shaped magnetic material is formedwith grooves or ridges so that dimples formed on the roll contactsurface thereof are divided by the grooves or ridges. This also makes itpossible to provide magnet shaving especially excellent magneticproperties.

[0034] Further, in this ribbon-shaped magnetic material, it is alsopreferred that the dimples produced on the roll contact surface of theribbon-shaped magnetic material upon solidification thereof include hugedimples each having an area equal to or greater than 2000 μm², in whichthe ratio of the area in the roll contact surface occupied by thusproduced huge dimples with respect to the total area of the roll contactsurface of the ribbon-shaped magnetic material is equal to or less than10%. Such ribbon-shaped magnetic material has less dispersion in crystalgrain sizes at various portions thereof, so that it is possible toprovide magnets having especially excellent magnetic properties.

[0035] Furthermore, in the ribbon shaped magnetic material, it is alsopreferred that the division of the dimples to be produced is carried outby transferring the shape of at least a part of the circumferentialsurface of the cooling roll to the roll contact surface of theribbon-shaped magnetic material. This also makes it possible to make thedispersion in the crystal grain sizes at the various portions of theribbon-shaped magnetic material small, so that it is possible to providemagnets having especially excellent magnetic properties.

[0036] In this case, it is preferred that the average thickness of theribbon-shaped magnetic material is 8-50 μm. By using such aribbon-shaped magnetic material, it is possible to provide magnetshaving more excellent magnetic properties.

[0037] Other aspect of the present invention is directed to a magneticpowder which is obtained by milling the ribbon-shaped magnetic materialwhich is manufactured by colliding a molten alloy to a circumferentialsurface of a cooling roll so as to cool and then solidify it, whereinthe circumferential surface of the cooling roll has dimple correctingmeans for dividing dimples to be produced on a roll contact surface ofthe ribbon-shaped magnetic material which is in contact with thecircumferential surface of the cooling roll.

[0038] By using such a magnetic powder, it is possible to providemagnets having excellent magnetic properties and reliability.

[0039] In this case, it is preferred that the magnetic powder issubjected to at least one heat treatment during or after themanufacturing process thereof. This makes it possible to provide magnetshaving more excellent magnetic properties.

[0040] Further, it is also preferred that the mean particle size of themagnetic powder lies within the range of 1-300 μm. This also makes itpossible to provide magnets having more excellent magnetic properties.

[0041] Furthermore, it is also preferred that the magnetic powder has acomposite structure which is composed of a hard magnetic phase and asoft magnetic phase. This also makes it possible to provide magnetshaving especially excellent magnetic properties.

[0042] In this case, it is preferred that the average crystal grain sizeof each of the hard magnetic phase and the soft magnetic phase is 1-100nm. This also makes it possible to provide magnets having excellentmagnetic properties, especially excellent coercive force andrectangularity.

[0043] The other aspect of the present invention is directed to a bondedmagnet which is manufactured by binding the magnetic powder which isobtained by milling the ribbon-shaped magnetic material which ismanufactured by colliding a molten alloy to a circumferential surface ofa cooling roll so as to cool and then solidify it, wherein thecircumferential surface of the cooling roll has dimple correcting meansfor dividing dimples to be produced on a roll contact surface of theribbon-shaped magnetic material which is in contact with thecircumferential surface of the cooling roll.

[0044] The bonded magnet manufactured as described above can haveespecially excellent magnetic properties and reliability.

[0045] In this case, it is preferred that the intrinsic coercive force(H_(CJ)) of the bonded magnet at a room temperature is in the range of320-1200 kA/m. This makes it possible to provide a bonded magnet havingexcellent heat resistance and magnetizability as well as sufficientmagnetic flux density.

[0046] In this case, it is preferred that the maximum magnetic energyproduct (BH)_(max) of the bonded magnet is equal to or greater than 40kJ/m³. By using such a bonded magnet, it is possible to provide highperformance small size motors.

[0047] These and other objects, structures and advantages of the presentinvention will be apparent from the following detailed description ofthe invention and the examples taken in conjunction with the appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 is a perspective view which schematically shows anapparatus (melt spinning apparatus) for manufacturing a ribbon-shapedmagnetic material equipped with a cooling roll of a first embodiment ofthe present invention.

[0049]FIG. 2 is a front view of the cooling roll shown in FIG. 1.

[0050]FIG. 3 is a sectional view which schematically shows the structureof a portion in the vicinity of the circumferential surface of thecooling roll shown in FIG. 1.

[0051]FIG. 4 is a cross-sectional view which schematically shows thestate caused at the vicinity of the colliding section of the moltenalloy with the cooling roll of the conventional melt spinning apparatuswhich manufactures a ribbon-shaped magnetic material by means of asingle roll method.

[0052]FIG. 5 is a cross-sectional view which schematically shows thestate caused at the vicinity of the colliding section of the moltenalloy with the cooling roll of the melt spinning apparatus shown in FIG.1.

[0053]FIG. 6 is a perspective view which schematically shows the surfacecondition of the ribbon-shaped magnetic material manufactured by theconventional melt spinning apparatus.

[0054]FIG. 7 is a perspective view which schematically shows the surfacecondition of the ribbon-shaped magnetic material manufactured by themelt spinning apparatus shown in FIG. 1.

[0055]FIG. 8 is an illustration for explaining a method of forming adimple correcting means.

[0056]FIG. 9 is an illustration for explaining another method of formingthe dimple correcting means.

[0057]FIG. 10 is an illustration which schematically shows one exampleof the composite structure (nanocomposite structure) of the magneticpowder of the present invention.

[0058]FIG. 11 is an illustration which schematically shows anotherexample of the composite structure (nanocomposite structure) of themagnetic powder of the present invention.

[0059]FIG. 12 is an illustration which schematically shows the otherexample of the composite structure (nanocomposite structure) of themagnetic powder of the present invention.

[0060]FIG. 13 is a front view which schematically shows a secondembodiment of the cooling roll according to the present invention.

[0061]FIG. 14 is a sectional view which schematically shows thestructure of a portion in the vicinity of the circumferential surface ofthe cooling roll shown in FIG. 13.

[0062]FIG. 15 is a front view which schematically shows a thirdembodiment of the cooling roll according to the present invention.

[0063]FIG. 16 is a sectional view which schematically shows thestructure of a portion in the vicinity of the circumferential surface ofthe cooling roll shown in FIG. 15.

[0064]FIG. 17 is a front view which schematically shows a fourthembodiment of the cooling roll according to the present invention.

[0065]FIG. 18 is a sectional view which schematically shows thestructure of a portion in the vicinity of the circumferential surface ofthe cooling roll shown in FIG. 17.

[0066]FIG. 19 is a front view which schematically shows other embodimentof the cooling roll according to the present invention.

[0067]FIG. 20 is a sectional view which schematically shows one exampleof the structure of the circumferential surface of the cooling roll ofthe present invention.

[0068]FIG. 21 is a sectional view which schematically shows anotherexample of the structure of the circumferential surface of the coolingroll of the present invention.

[0069]FIG. 22 is an electronograph of the surface condition of theribbon-shaped magnetic material according to the present invention.

[0070]FIG. 23 is a sectional side view which shows the situation causedat or around a colliding section of a molten alloy with a cooling rollin the conventional apparatus (melt spinning apparatus) whichmanufactures a ribbon-shaped magnetic material using a single rollmethod.

DETAILED DESCRIPTION OF THE INVENTION

[0071] Hereinbelow, embodiments of the cooling roll according to thepresent invention as well as embodiments of the ribbon-shaped magneticmaterial, magnetic powder and bonded magnet according to the presentinvention will be described in detail with reference to the accompanyingdrawings.

Structure of Melt Spinning Apparatus

[0072]FIG. 1 is a perspective view showing a melt spinning apparatuswhich manufactures a ribbon-shaped magnetic material using a single rollmethod. The apparatus is provided with a cooling roll 5 of a firstembodiment of the present invention. Further, FIG. 2 is a front view ofthe cooling roll shown in FIG. 1. and FIG. 3 is an enlarged sectionalview of a part of a circumferential surface of the cooling roll shown inFIG. 1.

[0073] As shown in FIG. 1, the melt spinning apparatus 1 Includes acylindrical body 2 capable of receiving a magnetic material, and acooling roll 5 which rotates in the direction of an arrow A in thefigure relative to the cylindrical body 2. A nozzle (orifice) 3 whichinjects the molten magnetic material (molten alloy) 6 is formed at thelower end of the cylindrical body 2.

[0074] The cylindrical body 2 may be formed of a heat resistance ceramicmaterial such as crystal, alumina, magnesia and the like.

[0075] The nozzle opening of the nozzle 3 may be formed in to variousshapes such as circle, ellipse, slit and the like.

[0076] In addition, on the outer periphery of the cylindrical body 2,there is provided a heating coil 4. By applying high frequency wave, forexample, the inside of the cylindrical body 2 is heated (inductivelyheated) and therefore the magnetic material in the cylindrical body 2becomes a melting state.

[0077] In this regard, it is to be noted that the heating means used inthis apparatus is not limited to the coil 4 described above, and acarbon heater may be employed instead of the coil 4.

[0078] The cooling roll 5 is constructed from a roll base 51 and asurface layer 52 which constitutes the circumferential surface 53 of thecooling roll 5.

[0079] The surface layer 52 may be formed from the same material as thatfor the roll base 51. However, it is preferred that the surface layer 52is formed from a material having a lower heat conductivity than that ofthe material for the roll base 51.

[0080] The material used for the roll base 51 is not limited to aspecific material. However, in the present invention, it is preferredthat the roll base 51 is formed from a metal material having a high heatconductivity such as copper or copper alloys in order to make itpossible to dissipate the heat generated in the surface layer 52 asquickly as possible.

[0081] The heat conductivity of the material of the surface layer 52 ator around a room temperature is not particularly limited to a specificvalue. However, it is preferable that the heat conductivity is equal toor less than 80 W·m⁻¹·K⁻¹, it is more preferable that the heatconductivity lies within the range of 3−60 W·m⁻¹·K⁻¹, and it is the mostpreferable that the heat conductivity lies within the range of 5−40W·m⁻¹·K⁻¹.

[0082] By constructing the cooling roll 5 from the surface layer 52 andthe roll base 51 each having the heat conductivity as described above,it becomes possible to quench the molten alloy 6 in an appropriatecooling rate. Further, the difference between the cooling rates at thevicinity of the roll contact surface 81 (which is a surface of the meltspun ribbon to be in contact with the circumferential surface of thecooling roll) and at the vicinity of the free surface 82 (which is asurface of the melt spun ribbon opposite to the roll contact surface)becomes small. Consequently, it is possible to obtain a melt spun ribbon8 having less dispersion in its crystal grain sizes at various portionsthereof and thereby having excellent magnetic properties.

[0083] Examples of the materials having such heat conductivity includemetal materials such as Zr, Sb, Ti, Ta, Pd, Pt and alloys of suchmetals, metallic oxides of these metals, and ceramics. Examples of theceramics include oxide ceramics such as Al₂O₃, SiO₂, TiO₂, Ti₂O₃, ZrO₂Y₂O₃, barium titanate, and strontium titanate and the like; nitrideceramics such as AlN, Si₃N₄, TiN, BN, ZrN, HfN, VN, TaN, NbN, CrN, Cr₂Nand the like; carbide ceramics such as graphite, SiC, ZrC, Al₄C₃, CaC₂,WC, TiC, HfC, VC, TaC, NbC and the like; and mixture of two or more ofthese ceramics. Among these ceramics, nitride ceramics and materialscontaining it are particularly preferred.

[0084] As compared with the conventional materials used for constitutingthe circumferential surface of the cooling roll (that is, Cu, Cr or thelike). these ceramics have high hardness and excellent durability(anti-abrasion characteristic). Therefore, even if the cooling roll 5 isrepeatedly used, the shape of the circumferential surface 53 can bemaintained, and therefore the effect of the dimple correcting means(described later) will be scarcely deteriorated.

[0085] Further, normally, the materials which can be used for thecooling roll 51 described above have high coefficient of thermalexpansion. Therefore, it is preferred that the coefficient of thermalexpansion of the material of the surface layer 52 is close to that ofthe material of the roll base 51. For example, the coefficient ofthermal expansion (coefficient of linear expansion a) at or around aroom temperature is preferably in the range of 3.5−18[×10⁻⁶K⁻¹], andmore preferably in the range of 6−12[×10⁻⁶K⁻¹]. When the coefficient ofthermal expansion of the material of the surface layer 52 at or around aroom temperature lies within this range, it is possible to maintainreliable bonding between the roll base 51 and the surface layer 52,thereby enabling to prevent peeling-off of the surface layer 52effectively.

[0086] The surface layer 52 may be formed in to a laminate structurehaving a plurality of layers of different compositions, besides thesingle layer structure described above. For example, such a surfacelayer 52 may be formed from two or more layers which include a layer ofthe metallic material and a layer of the ceramic material describedabove. Example of such a two layer laminate structure of the surfacelayer 52 includes a laminate composed of a lower layer of the metallicmaterial located at the side of the roll base 51 and an upper layer ofthe ceramic material. In this case, it is preferred that these adjacentlayers are well adhered or bonded to each other. For this purpose, theseadjacent layers may contain the same element therein.

[0087] Further, when the surface layer 52 is formed into such a laminatestructure comprised of a plurality of layers, it is preferred that atleast the outermost layer is formed from the material having the heatconductivity within the range described above.

[0088] Furthermore, in the case where the surface layer 52 is formedinto the single layer structure described above, it is not necessary forthe composition of the material of the surface layer to have uniformdistribution in the thickness direction thereof. For example, thecontents of the constituents may be gradually changed in the thicknessdirection thereof (that is, graded materials may be used).

[0089] The average thickness of the surface layer 52 (in the case of thelaminate structure, the total thickness thereof) is not limited to aspecific value. However, it is preferred that the average thickness lieswithin the range of 0.5-50 μm, and more preferably 1-20 μm.

[0090] If the average thickness of the surface layer 52 is less than thelower limit value described above, there is a possibility that thefollowing problems will be raised. Namely, depending on the material tobe used for the surface layer 52, there is a case that cooling abilitybecomes too high. When such a material is used for the surface layer 52,a cooling rate becomes too large in the vicinity of the roll contactsurface 81 of the melt spun ribbon 8 even though it has a considerablylarge thickness, thus resulting in the case that amorphous structure beproduced at that portion. On the other hand, in the vicinity of the freesurface 82 of the melt spun ribbon 8 where the heat conductivity isrelatively low, the cooling rate becomes small as the thickness of themelt spun ribbon 8 increases, so that crystal grain size is liable to becoarse. Namely, this leads to the case that the crystal grain size isliable to be coarse in the vicinity of the free surface 82 of theobtained melt spun ribbon 8 and that amorphous structure Is liable to beproduced in the vicinity of the roll contact surface 81 of the melt spunribbon 8, which results in the case that satisfactory magneticproperties can not be obtained. In this regard, even if the thickness ofthe melt spun ribbon 8 is made small by increasing the peripheralvelocity of the cooling roll 5, for example, in order to reduce thecrystal grain size in the vicinity of the free surface 82 of the meltspun ribbon 8, this in turn leads to the case that the melt spun ribbon8 has more random amorphous structure in the vicinity of the rollcontact surface 81 of the obtained melt spun ribbon 8. In such a meltspun ribbon 8, there is a case that sufficient magnetic properties willnot be obtained even if it is subjected to a heat treatment aftermanufacturing thereof.

[0091] On the other hand, if the average thickness of the surface layer52 exceeds the above upper limit value, the cooling rate becomes slowand thereby the crystal grain size becomes coarse, thus resulting in thecase that magnetic properties become poor.

[0092] The method for forming the surface layer 52 is not limited to aspecific method. However, it is preferable to employ a chemical vapordeposition (CVD) method such as heat CVD, plasma CVD, and laser CVD andthe like, or a physical vapor deposition method (PVD) such as vapordeposition, spattering and ion-plating and the like. According to thesemethods, it is possible to obtain a surface layer having an uniformthickness with relative ease, so that it is not necessary to performmachining work onto the surface thereof after formation of the surfacelayer 52. Further, the surface layer 52 may be formed by means of othermethod such as electro plating, immersion plating, elecroless plating,and metal spraying and the like. Among these methods, the metal sprayingis particularly preferred. This is because when the surface layer 52 isformed by means of the method, the surface layer 52 can be firmlyadhered or bonded to the roll base 51.

[0093] Further, prior to the formation of the surface layer 52 onto theouter circumferential surface of the roll base 51, a pre-treatment maybe made to the outer surface of the roll base 51. Examples of such apre-treatment include washing treatment such as alkaline wash, oxidewash and wash using organic solvent and the like, and primer treatmentsuch as blasting, etching and formation of a plating layer and the like.In this way, the surface layer 52 is more firmly bonded with the rollbase 51 after the formation of the surface layer 52. In addition, bycarrying out the primer treatment as described above, it becomespossible to form an uniform and precise surface layer 52, so that theobtained cooling roll 5 has less dispersion in its heat conductivitiesat various portions thereof.

Dimple Correcting Means

[0094] As described later, the melt spun ribbon 8 is manufactured bycolliding a molten alloy 6 of a magnetic material onto thecircumferential surface 53 of the cooling roll 5 to quench (cool) it. Atthis time, there is case that dimples are produced or formed on the rollcontact surface 81 of the melt spun ribbon 8 since gas has enteredbetween the circumferential surface 53 and the puddle 7 of the moltenalloy 6. As shown in FIG. 4, since portions to which gas has entered arecooled with the state that the gas is being stored therein, dimples areformed on the roll contact surface 81 of the obtained melt spun ribbon 8(see FIG. 6). Further, the portions of the puddle 7 which are in contactwith the entered gas have relatively smaller cooling rate as comparedwith other portions of the puddle 7, thus leading to coarse of crystalgrain sizes. As a result, the obtained melt spun ribbon 8 has largevariations or dispersions in its crystal grain sizes and magneticproperties. This tendency becomes prominent as the area of each dimple 9and the total area of the dimples 9 become large.

[0095] In view of the above problem, in the circumferential surface 53of the cooling roll 5 of the present invention, there is provided dimplecorrecting means for dividing dimples 9 to be produced on the rollcontact surface 81 of the melt spun ribbon 8. By providing such dimpledividing means on the cooling roll 5, dimples 9 are produced or formedwith a state that they are divided by the grooves 84 as shown in FIGS. 5and 7. Further, due to the gas expelling effect by the grooves 84(described later), at least a part of the gas which has entered betweenthe circumferential surface 53 and the puddle 7 is expelled through thegrooves 54, an amount of the gas remaining between the circumferentialsurface 53 and the puddle 7 becomes small. For these reasons, the areaof each of dimples produced on the roll contact surface 81 of theobtained melt spun ribbon 8 becomes small, and therefore the total areaof the produced dimples also becomes small (see FIG. 7). This means thatthe dispersion in the cooling rates at the various portions of thepuddle 7 becomes small, so that it is possible to obtain a melt spunribbon having small dispersion In its crystal grain sizes and havingexcellent magnetic properties.

[0096] In the example shown in the drawings, the dimple correcting meansis constructed from grooves 54 formed in the circumferential surface 53of the cooling roll 5 in parallel with the rotational direction of thecooling roll 5. In this connection, it is to be noted that between theadjacent grooves 54, ridges 55 are existed. In the present invention,thus formed ridges 55 function as the dimple correcting means.

[0097] By forming such grooves 54 in the circumferential surface 53 ofthe cooling roll 5, the gas that has entered between the circumferentialsurface 53 and the puddle 7 1s capable of entering the grooves 54 andthen flowing through the grooves 54. Therefore, the gas that has enteredbetween the circumferential surface 53 and the puddle 7 is expelledthrough the grooves in accordance with the rotation of the cooling roll5. Due to such effect (hereinafter, referred to as “gas expellingeffect”), the puddle 7 becomes brought into contact with thecircumferential surface 53 at the portions where the gas has entered.When the puddle 7 contacts with the circumferential surface 53 in thisway, dimples 9 are produced with a state that they are divided by theridges 55 as shown in FIG. 7, so that the area of each of the dimplesbecomes small. In addition, the amount of the gas remaining between thepuddle 7 and the circumferential surface 53 becomes small, the totalarea of the produced dimples also become small. As a result, dispersionin the cooling rates at various portions of the puddle 7 becomes small,so that it becomes possible to obtain a melt spun ribbon 8 having smalldispersion in its crystal grain sizes and having excellent magneticproperties.

[0098] In this connection, it is to be noted that although in theexample shown in the drawings a plurality of ridges 55 are formed, atleast one ridge is sufficient in this invention

[0099] The average value of the widthL_(1 of each groove 54 (the width of the groove at an opening portion in the circumferential surface 53) is preferably set to be)0.5-90 μm, and more preferably 1-50 μm. If the average value of thewidth L₁ of the groove 54 is less than the smallest value, the gasexpelling effect for expelling the gas which has entered between thecircumferential surface 53 and the puddle 7 is lowered. On the otherhand, if the average value of the width L₁ of the groove 54 exceeds thelargest value, there is a case that large dimples are produced at theportions of the grooves 54 so that the crystal grain size becomescoarse.

[0100] Further, the average value of the width L₂ of the ridge 55 (atthe maximum width portion of the ridge) is preferably set to be 0.5 to95 μm, and more preferably 1 to 50 μm. If the average value L₂ of theridge 55 is less than the lowest value, the ridges will not function asthe dimple correcting means sufficiently, so that there is a case thathuge dimples are formed on the roll contact surface. On the other hand,if the average value L₂ of the ridge 55 exceeds the above upper limitvalue, the surface area of the ridges becomes too large, thus resultingin the case that dimples are formed between the ridges and the puddle.

[0101] The average value of the depth (maximum depth) L₃ of each groove54 (or the average value of the maximum height of the ridge L₃ of eachridge 55) is preferably set to be 0.5-20 μm, and more preferably 1-10μm. If the average value of the depth L₃ of the groove 54 is less thanthe smallest value, there is a case that the gas expelling effect forexpelling the gas which has entered between the circumferential surface53 and the puddle 7 Is lowered so that the effect as the dimplecorrecting means can not be sufficiently exhibited. On the other hand,if the average value of the depth L3 of the groove 54 exceeds thelargest value, the flow rate of the gas flowing in the groove increasesso that the gas flow tends to be turbulent flow with eddies, whichresults in the case that the effect of the dimple correcting means cannot be sufficiently exhibited.

[0102] The average value of the pitch L₄ between the adjacent grooves 54(or the average value of the pitch L₄ between the adjacent ridges 55) isan important factor for adjusting or determining the size of each ofdimples 9 to be formed on the roll contact surface 81 of the melt spunribbon 8 as well as the total area of the formed dimples 9. Preferably,the average value of the pitch L₄ between the adjacent grooves 54 (orthe average value of the pitch L₄ between the adjacent ridges 55) is setto be 0.5-100 μm, and more preferably 3-50 μm. If the average value ofthe pitch L ₄ is within this range, each ridge 55 effectively functionsas the dimple correcting means, and the interval between the contactingportion and the non-contacting portion of the circumferential surface 53with respect to the puddle 7 can be made sufficiently small. With thisresult, the difference in the cooling rates between the portions of thepuddle that are in contact with the cooling roll 5 and the portions ofthe puddle that do not contact with the cooling rolls becomessufficiently small, so that it is possible to obtain a melt spun ribbon8 having small dispersion in its grain sizes and magnetic properties.

[0103] The ratio of the area of the grooves 54 (or ridges 55) withrespect to the area of the circumferential surface 53 when they areprojected on the same plane should preferably be equal to or larger than10%, and more preferably lies in the range of 30-99.5%. If the ratio ofthe projected area of the grooves 54 (or ridges 55) with respect to theprojected area of the circumferential surface 53 is less than 10%, it isnot possible to provide sufficient gas expelling flow paths forexpelling the gas that has entered between the puddle 7 and thecircumferential surface 53, so that the gas is liable to remain betweenthe puddle 7 and the circumferential surface 53, thus leading to thecase that huge dimples be produced.

[0104] Various methods can be used for forming the grooves 54 (or ridges55) in the circumferential surface 53 of the cooling roll 5. Examples ofthe methods include various machining processes such as cutting,transfer (pressure rolling), gliding, blasting and the like, laserprocessing, electrical discharge machining, and chemical etching and thelike. Among these methods, the machining process, especially gliding isparticularly preferred, since according to the gliding the width anddepth of each groove and the pitch of the adjacent grooves can berelatively easily adjusted with high precision as compared with othermethods.

[0105] In this connection, it is to be noted that the ridges 55 areconstructed from the resulting form of the circumferential surface 53which are obtained after the grooves 54 have been formed in thecircumferential surface 53 by the method mentioned above.

[0106] In the case where the surface layer 52 is provided on the outercircumferential surface of the roll base 51 (that is, the case where thesurface layer 52 is not integrally formed with the roll base 51), thegrooves 54 and ridges 55 may be directly formed in the surface layer 52by means of the method described above, or may be formed by using otherway. Specifically, as shown in FIG. 8, after the formation of thesurface layer 52, the grooves 54 and ridges 55 can be formed in thesurface layer 52 by means of the method described above. Alternatively,as shown in FIG. 9, it is also possible to form grooves 54 and ridges 55onto the outer circumferential surface of the roll base 51 by means ofthe method described above, and then to form a surface layer 52 thereon.In the latter way, the thickness of the surface layer 52 is made smallin comparison with the depth of each groove 54 or the height of eachridge 55 formed in the roll base 51. With this result, the ridges 55acting as the dimple correcting means can be formed in thecircumferential surface 53 without performing any machining work for thesurface of the surface layer 52. According to this way, since nomachining work is performed for the surface of the surface layer 52, thesurface roughness Ra of the circumferential surface 53 can be madeconsiderably small without polishing which is normally made in the finalstage.

[0107] In this connection, it is to be noted that in each of FIG. 3 andFIG. 5 a boundary surface between the roll base and the surface layer isomitted from the drawing (in each of FIGS. 14, 16, 18, 20 and 21 ofwhich explanation will be made later, a boundary surface is alsoomitted).

Alloy Composition of Magnetic Material

[0108] In this invention, it is preferred that the ribbon-shapedmagnetic material and the magnetic powder according to the presentinvention have excellent magnetic properties. For this purpose, it ispreferred that they are formed from alloys containing R (here, R is atleast one of the rare-earth elements containing Y). Among these alloys,alloys containing R (here, R is at least one of the rare-earth elementscontaining Y), TM (here, TM is at least one of transition metals) and B(Boron) are particularly preferred. In this case, any one of thefollowing alloys is preferably used.

[0109] (1) An alloy containing as basis components thereof a rare-earthelement mainly containing Sm and a transition meal mainly containing Co(hereinafter, referred to “as Sm—Co based alloys”).

[0110] (2) An alloy containing as basic components thereof R (here, R isat least one of the rare-earth elements containing Y), a transitionmetal mainly containing Fe (TM) and B (hereinafter, referred to as“R-TM-B based alloys”).

[0111] (3) An alloy containing as basic components thereof a rare-earthelement mainly containing Sm, a transition metal mainly containing Feand an interstitial element mainly containing N (hereinafter, referredto as “Sm—Fe—N based alloys”).

[0112] (4) An alloy containing as basic components thereof R (here, R isat least one of the rare-earth elements containing Y) and a transitionmeal such as Fe, and having a nanocomposite structure in which a softmagnetic phase and a hard magnetic phase are adjacently existed(including the case where they are adjoined through an intergranularboundary phase).

[0113] (5) A mixture of two or more of the above-mentioned alloycompositions (1) to (4). In this case, the advantages of the alloycompositions to be mixed can be enjoyed, so that more excellent magneticproperties can be obtained easily.

[0114] Typical examples of the Sm—Co based alloys include SmCo₅, Sm₂TM₁₇(here, TM is a transition metal).

[0115] Typical examples of the R—Fe—B based alloys include Nd—Fe—B basedalloys, Pr—Fe—B based alloys, Nd—Pr—Fe—B based alloys, Nd—Dy—Fe—B basedalloys. Ce—Nd—Fe—B based alloys, Ce—Pr—Nd—Fe—B based alloys, and one ofthese alloys in which a part of Fe is substituted by other transitionmetal such as Co or Ni or the like.

[0116] Typical examples of the Sm—Fe—N based alloys include Sm₂Fe₁₇N₃which is formed by nitrifying a Sm₂Fe₁₇ alloy and Sm—Zr—Fe—Co—N basedalloys having a TbCu₇ phase. In this regard, in the case of the Sm—Fe—Nbased alloys, normally N is introduced with the form of interstitialatom by subjecting the melt spun ribbon to an appropriate heat treatmentto nitrify it after the melt spun ribbon has been manufactured.

[0117] In this connection, examples of the rare-earth elements mentionedabove include Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho. Er, Tm, Yb,Lu, and a misch metal, and one or more of these rare-earth metals may becontained. Further, examples of the transition metals include Fe, Co, Niand the like, and one or more of these metals may be contained.

[0118] Further, in order to enhance magnetic properties such as coerciveforce and maximum energy product and the like, or in order to improveheat resistance and corrosion resistance, the magnetic materials maycontain one or more of Al, Cu, Ga, Si, Ti, V, Ta, Zr, Nb, Mo, Hf, Ag,Zn, P, Ge, Cr and W, as needed.

[0119] In this composite structure (nanocomposite structure), a softmagnetic phase 10 and a hard magnetic phase 11 exist with a pattern(model) as shown in, for example, FIG. 10. FIG. 11 or FIG. 12, in whichthe thickness of the respective phases and the grain sizes therein areon the order of nanometers. Further, the soft magnetic phase 10 and thehard magnetic phase 11 are arranged adjacent to each other (this alsoincludes the case where these phases are adjacent through intergranularboundary phase), which makes it possible to perform magnetic exchangeinteraction therebetween.

[0120] The magnetization of the soft magnetic phase readily changes itsorientation by the action of an external magnetic field. Therefore, whenthe soft magnetic phase coexists with the hard magnetic phase, themagnetization curve for the entire system shows a stepped “serpentinecurve” in the second quadrant of the B-H diagram (J-H diagram). However,when the soft magnetic phase has a sufficiently small size of less thanseveral tens of nm, magnetization of the soft magnetic phase issufficiently and strongly constrained through the coupling with themagnetization of the surrounding hard magnetic phase, so that the entiresystem exhibits functions like a hard magnetic material.

[0121] A magnet having such a composite structure (nanocompositestructure) has mainly the following five features.

[0122] (1) In the second quadrant of the B-H diagram (J-H diagram), themagnetization springs back reversively (in this sense, such a magnet isalso referred to as a “spring magnet”).

[0123] (2) It has a satisfactory magnetizability, so that it can bemagnetized with a relatively low magnetic field.

[0124] (3) The temperature dependence of the magnetic properties issmall as compared with the case where the system is constituted from ahard magnetic phase alone.

[0125] (4) The changes in the magnetic properties with the elapse oftime are small.

[0126] (5) No deterioration in the magnetic properties is observableeven if it is finely milled.

[0127] As described above, the magnets composed of the compositestructure have excellent magnetic properties. Therefore, it is preferredthat the magnetic powders according to the present invention have such acomposite structure.

[0128] In this regard, it is to be understood that the patterns shown inFIGS. 10 to 12 are mere examples, and the composite structure is notlimited thereto.

Manufacture of Ribbon-shaped Magnetic Material

[0129] Hereinbelow, description will be made with regard to themanufacturing of the ribbon-shaped magnetic material (that is, melt spunribbon) using the cooling roll 5 described above.

[0130] As described above, the ribbon-shaped magnetic material ismanufactured by colliding a molten alloy of the magnetic material ontothe circumferential surface of the cooling roll to cool and thensolidify it. Hereinbelow, one example thereof will be described.

[0131] As shown in FIG. 1, the melt spinning apparatus 1 is installed ina chamber (not shown), and it is operated under the condition where theinterior of the chamber is filled with an inert gas or other kind ofambient gas. In particular, in order to prevent oxidation of a melt spunribbon 8, it is preferable that the ambient gas is an inert gas.Examples of such an inert gas include argon gas, helium gas, nitrogengas or the like.

[0132] The pressure of the ambient gas is not particularly limited to aspecific value, but 1-760 Torr is preferable.

[0133] A predetermined pressure which is higher than the internalpressure of the chamber is applied to the surface of the liquid of themolten alloy 6 in the cylindrical body 2. The molten alloy 6 is injectedfrom the nozzle 3 by the differential pressure between the pressure ofthe ambient gas in the chamber and the summed pressure of the pressureapplied to the surface of the liquid of the molten alloy 6 in thecylindrical body 2 and the pressure exerted in the cylindrical body 2 inproportion to the liquid level.

[0134] The molten alloy injecting pressure (that is, the differentialpressure between the pressure of the ambient gas in the chamber and thesummed pressure of the pressure applied to the surface of the liquid ofthe molten alloy 6 in the cylindrical body 2 and the pressure exerted inthe cylindrical body 2 in proportion to the liquid level) is notparticularly limited to a specific value, but 10-100 kPa is preferable.

[0135] In the melt spinning apparatus 1, a magnetic material (alloy) isplaced in the cylindrical body 2 and it is melted by heating with thecoil 4, and then the molten alloy 6 is discharged from the nozzle 3.Then, as shown in FIG. 1, the molten alloy 6 collides with thecircumferential surface 53 of the cooling roll 5, and after theformation of a puddle 7, the molten alloy 6 is cooled down rapidly to besolidified while being dragged along the circumferential surface 53 ofthe rotating cooling roll 5, thereby forming a melt spun ribbon 8continuously or intermittently. Under the situation, if gas (ambientgas) enters between the puddle 7 and the circumferential surface 53,dimples 9 are produced on the roll contact surface of the melt spunribbon 8, as described above. However, in this embodiment, since thedimple correcting means (ridges 55) is provided in the circumferentialsurface 53 of the cooling roll 5, these dimples are produced with astate that they are divided by the grooves formed on the roll contactsurface. The melt spun ribbon 8 thus formed is soon released from thecircumferential surface 53, and the melt spun ribbon 8 proceeds in thedirection of an arrow B in FIG. 1.

[0136] Since the dimple correcting means is provided in thecircumferential surface 53 of the cooling roll 5 in this way, formationof huge dimples is prevented and thereby ununiform cooling of the puddle7 is also prevented. As a result, it is possible to obtain a melt spunribbon 8 having less dispersion In its crystal grain sizes and havingexcellent magnetic properties.

[0137] In this connection, it is to be noted that when manufacturingsuch a melt spun ribbon 8, it is not always necessary to install thenozzle 3 just above the rotation axis 50 of the cooling roll 5.

[0138] The optimum range of the peripheral velocity of the cooling roll5 depends upon the composition of the molten alloy, the structuralmaterial (composition) of the surface layer 52, and the surfacecondition of the circumferential surface 53 (especially, the wettabilityof the circumferential surface 53 with respect to the molten alloy 6),and the like. However, for the enhancement of the magnetic properties, aperipheral velocity in the range of 5 to 60 m/s is normally preferable,and 10 to 40 m/s is more preferable. If the peripheral velocity of thecooling roll 5 is less than the above lower limit value, the coolingrate of the molten alloy 6 (puddle 7) is decreased. This tends toincrease the crystal grain size, thus leading to the case that themagnetic properties are lowered. On the other hand, when the peripheralvelocity of the cooling roll 5 exceeds the above upper limit value, thecooling rate is too high, and thereby amorphous structure becomesdominant. In this case, there is a case that the magnetic properties cannot be sufficiently improved even if a heat treatment described below isgiven in the later stage.

[0139] It is preferred that thus obtained melt spun ribbon 8 has uniformwidth w and thickness t In this case, the average thickness t of themelt spun ribbon 8 should preferably lie in the range of 8-50 μm andmore preferably lie in the range of 10-40 μm. If the average thickness tis less than the lower limit value, amorphous structure becomesdomenant, so that there is a case that the magnetic properties can notbe sufficiently improved even if a heat treatment is given in the laterstage. Further, productivity per a unit time is also lowered. On theother hand, if the average thickness t exceeds the above upper limitvalue, the crystal grain size at the side of the free surface 82 of themelt spun ribbon 8 tends to be coarse, so that there is a case that themagnetic properties are lowered.

[0140] In the spun ribbon 8 of the present invention obtained asdescribed above, the surface shape or form of the circumferentialsurface 53 of the cooling roll 5 is transferred (completely orpartially) to at least a part of the roll contact surface 81 of the meltspun ribbon 8. Consequently, on the roll contact surface 81 of the meltspun ribbon 8, ridges 83 and grooves (or recesses) 84 which respectivelycorrespond to the surface shape of the circumferential surface 53 of thecooling roll 5 (that is, the grooves 54 and ridges 55) are formed. Sincethe ridges 83 and grooves 84 are formed on the roll contact surface 81of the melt spun ribbon 8 in this way, dimples are produced with a statethat they are effectively divided by these grooves 84 such that the areaof each of the dimples is small. Further, the total area of the dimples9 is also decreased because of the gas expelling effect by the grooves54 formed in the circumferential surface 53 of the cooling roll 5, asdescribed above. With this result, it is possible to obtain a melt spunribbon 8 having less dispersion in its crystal grain sizes at variousportions thereof and having excellent magnetic properties.

[0141] Further, in the present invention, it is preferred that the ratioof the projected area of huge dimples 9 (here, a huge dimple means adimple having an area more than 2000 μm²) which are formed on the rollcontact surface 81 of the melt spun ribbon 8 upon solidification thereofis less than 10%, and more preferably less than 5%. If the ratio exceeds10%, the total area of portions of the melt spun ribbon 8 havingextremely small cooling rate (that is, portions of the roll contactsurface 81 of the melt spun ribbon 8 where the huge dimples are formed,in particular a part around the center of each huge dimple) becomeslarge as compared with the total area of portions of the melt spunribbon 8 that are in contact with the cooling roll 5, so that magneticproperties of the melt spun ribbon 8 are lowered as a whole.

[0142] In this regard, it is to be noted that the ratio of the projectedarea of the huge dimples 9 is calculated as a ratio of the projectedarea with respect to a predetermined area on the roll contact surface81. In this case, it is preferred that the ratio is an average valueobtained from several sampling points on the roll contact surface 81.

[0143] Further, in the present invention, it is preferred that the ratioof the projected area of dimples 9 (all dimples) which are formed on theroll contact surface 81 of the melt spun ribbon 8 upon solidificationthereof is less than 40%, and more preferably less than 30%. If theratio of the projected area of the dimples is too large, the coolingrate upon solidification is lowered as a whole, so that crystal grainsize becomes coarse and thereby magnetic properties of the obtained meltspun ribbon is also lowered.

[0144] Furthermore, the obtained melt spun ribbon 8 may be subjected toat least one heat treatment for the purpose of, for example,acceleration of recrystallization of the amorphous structure andhomogenization of the structure. The conditions of this heat treatmentmay be, for example, a heating in the range of 400 to 900° C. for 0.2 to300 min.

[0145] Moreover, in order to prevent oxidation, it is preferred thatthis heat treatment is performed in a vacuum or under a reduced pressure(for example, in the range of 1×10⁻¹ to 1×10⁻⁶ Torr), or in anonoxidizing atmosphere of an inert gas such as nitrogen gas, argon gas,helium gas or the like.

[0146] The melt spun ribbon (ribbon-shaped magnetic material) 8 obtainedas in the above has a microcrystalline structure or a structure In whichmicrocrystals are included in an amorphous structure, and exhibitsexcellent magnetic properties.

[0147] In the foregoing, the description was made with reference to thesingle roll method. However, it is of course possible to use a twin rollmethod. According to these quenching methods, the metallic structure(that is, crystal grain) can be formed into microstructure, so thatthese methods are particularly effective in improving magneticproperties of bonded magnets. especially coercive force thereof.

Manufacture of Magnetic Powder

[0148] The magnetic powder of this invention is obtained by milling themelt spun ribbon 8 which is manufactured as described above.

[0149] The milling method of the melt spun ribbon is not particularlylimited, and various kinds of milling or crushing apparatus such as ballmill, vibration mill, jet mill, and pin mill maybe employed. In thiscase, in order to prevent oxidation, the milling process may be carriedout in vacuum or under a reduced pressure (for example, under a reducedpressure of 1×10⁻¹ to 1×10⁻⁶ Torr), or in a nonoxidizing atmosphere ofan inert gas such as nitrogen, argon, helium, or the like.

[0150] The average particle size (diameter) of the magnetic powder isnot particularly limited. However, in the case where the magnetic powderis used for manufacturing bonded magnets (rare-earth bonded magnets)described later, in order to prevent oxidation of the magnetic powderand deterioration of the magnetic properties during the milling process,it is preferred that the average particle size lies within the range of1 to 300 μm, more preferably within the range of 5 to 150 μum.

[0151] In order to obtain a better moldability of the bonded magnet, itis preferable to give a certain degree of dispersion to the particlesize distribution of the magnetic powder. By so doing, it is possible toreduce the void ratio (porosity) of the bonded magnet obtained. As aresult, it is possible to increase the density and the mechanicalstrength of the bonded magnet as compared with a bonded magnet havingthe same content of the magnetic powder, thereby enabling to furtherimprove the magnetic properties.

[0152] Thus obtained magnetic powder may be subjected to a heattreatment for the purpose of, for example, removing the influence ofstress introduced by the milling process and controlling the crystalgrain size. The conditions of the heat treatment are, for example,heating at a temperature In the range of 350 to 850° C. for 0.2 to 300min

[0153] In order to prevent oxidation of the magnetic powder, it ispreferable to perform the heat treatment in a vacuum or under a reducedpressure (for example, in the range of 1×10⁻¹ to 1×10⁻⁶ Torr), or in anonoxidizing atmosphere of an inert gas such as nitrogen gas, argon gas,and helium gas.

[0154] Thus obtained magnetic powder has a satisfactory bindability withbinding resins (wettability of binding resins). Therefore, when a bondedmagnet is manufactured using the magnetic powder described above, thebonded magnet has high mechanical strength as well as excellent thermalstability (heat resistance) and corrosion resistance. Consequently, itcan be concluded that the magnetic powder is suitable for themanufacture of the bonded magnet, and the manufactured bonded magnet hashigh reliability.

[0155] In such magnetic powder as described above, the average crystalgrain size of the magnetic powder should preferably be equal to or lessthan 500 nm, more preferably equal to or less than 200 nm, and mostpreferably lie in the range of 10-120 nm. If the average crystal grainsize exceeds 500 nm, there is a case that magnetic properties,especially coercive force and rectangularity can not be sufficientlyimproved.

[0156] In particular, when the magnetic material is an alloy having thecomposite structure as described (4) in the above, the average crystalgrain size should preferably lie in the range of 1-100 nm, and morepreferably lie in the range of 5-50 nm. When the average crystal grainsize lies in this range, more effective magnetic exchange interactionoccurs between the soft magnetic phase 10 and the hard magnetic phase11,so that markedly improved magnetic properties can be recognized.

Bonded Magnet and Manufacturing thereof

[0157] Hereinbelow, a description will be made with regard to the bondedmagnet according to the present invention

[0158] The bonded magnet according to the present invention ismanufactured by binding the magnetic powder described above using abinding resin (binder)

[0159] As for the binder, either of a thermoplastic resin or athermosetting resin may be employed.

[0160] Examples of the thermoplastic resin include polyamid (example:nylon 6, nylon 46, nylon 66, nylon 610, nylon 612. nylon 11, nylon 12,nylon 6-12, nylon 6-66); thermoplastic polyimide; liquid crystal polymersuch as aromatic polyester; poly phenylene oxide, poly phenylenesulfide; polyolefin such as polyethylene, polypropylene andethylene-vinyl acetate copolymer; modified polyolefin; polycarbonate;poly methyl methacrylate; polyester such as poly ethylen terephthalateand polybutylene terephthalate; polyether; polyether ether ketone;polyetherimide; polyacetal; and copolymer, blended body, and polymeralloy having at least one of these materials as a main ingredient. Inthis case, a mixture of two or more kinds of these materials may beemployed.

[0161] Among these resins, a resin containing polyamide as its mainingredient is particularly preferred from the viewpoint of especiallyexcellent moldability and high mechanical strength. Further, a resincontaining liquid crystal polymer and/or poly phenylene sulfide as itsmain ingredient is also preferred from the viewpoint of enhancing theheat resistance. Furthermore, these thermoplastic resins also have anexcellent kneadability with the magnetic powder.

[0162] These thermoplastic resins provide an advantage in that a widerange of selection can be made. For example, it is possible to provide athermoplastic resin having a good moldability or to provide athermoplastic resin having good heat resistance and mechanical strengthby appropriately selecting their kinds, copolymerization or the like.

[0163] On the other hand, examples of the thermosetting resin includevarious kinds of epoxy resins of bisphenol type, novolak type, andnaphthalene-based, phenolic resins, urea resins, melamine resins,polyester (or unsaturated polyester) resins, polyimide resins, siliconeresins, polyurethane resins, and the like. In this case, a mixture oftwo or more kinds of these materials may be employed.

[0164] Among these resins, the epoxy resins, phenolic resins, polyimideresins and silicone resins are preferable from the viewpoint of theirspecial excellence in the moldability, high mechanical strength, andhigh heat resistance. In these resins, the epoxy resins are especiallypreferable. These thermosetting resins also have an excellentkneadability with the magnetic powder and homogeneity (uniformity) inkneading.

[0165] The unhardened thermosetting resin to be used may be either in aliquid state or in a solid (powdery) state at a room temperature.

[0166] The bonded magnet according to this invention described in theabove may be manufactured, for example, as in the following. First, themagnetic powder, a binding resin and an additive (antioxidant,lubricant, or the like) as needed are mixed and kneaded (e.g. warmkneading) to form a bonded magnet composite (compound). Then, thusobtained bonded magnet composite is formed into a desired magnet form ina space free from magnetic field by a molding method such as compactionmolding (press molding), extrusion molding, or injection molding. Whenthe binding resin used is a thermosetting type, the obtained greencompact is hardened by heating or the like after molding.

[0167] In these three types of molding methods, the extrusion moldingand the injection molding (in particular, the injection molding) haveadvantages in that the latitude of shape selection is broad and theproductivity is high, for example. However, these molding methodsrequire to ensure a sufficiently high fluidity of the compound in themolding machine in order to obtain satisfactory moldability. For thisreason, In these methods it is not possible to increase the content ofthe magnetic powder, namely, it is not possible to make bonded magnetshaving high density, as compared with the case of the compaction moldingmethod. In this invention, however, it is possible to obtain a highmagnetic flux density as will be described later, so that excellentmagnetic properties can be obtained even without making the bondedmagnet high density. This advantage of the present invention can also beextended even in the case where bonded magnets are manufactured by theextrusion molding method or the injection molding method.

[0168] The content of the magnetic powder in the bonded magnet is notparticularly limited, and it is normally determined by considering thekind of the molding method to be used and the compatibility ofmoldability and high magnetic properties. For example, it is preferredthat the content is in the range of 75-99.5 wt %, and more preferably inthe range of 85-97.5 wt %.

[0169] In particular, in the case of a bonded magnet manufactured by thecompaction molding method, the content of the magnetic powder shouldpreferably lie in the range of 90-99.5 wt %, and more preferably in therange of 93-98.5 wt %.

[0170] Further, in the case of a bonded magnet manufactured by theextrusion molding or the injection molding, the content of the magneticpowder should preferably lie in the range of 75-98 wt %, and morepreferably in the range of 85-97 wt %.

[0171] The density p of the bonded magnet is determined by factors suchas the specific gravity of the magnetic powder contained in the bondedmagnet and the content of the magnetic powder, and the void ratio(porosity) of the bonded magnet and the like. In the bonded magnetsaccording to this invention, the density ρ is not particularly limitedto a specific value, but it is preferable to be in the range of 4.5-6.6Mg/m³, and more preferably in the range of 5.5-6.4 Mg/m³.

[0172] In this invention, since the remanent magnetic flux density andthe coercive force of the magnetic powder are high, the bonded magnetformed from the magnetic powder provides excellent magnetic properties(especially, high maximum magnetic energy product (BH)_(max)) even whenthe content of the magnetic powder is relatively low. In this regard, itgoes without saying that it is possible to obtain the excellent magneticproperties in the case where the content of the magnetic powder is high.

[0173] The shape, dimensions and the like of the bonded magnetmanufactured according to this invention are not particularly limited.For example, as to the shape, all shapes such as columnar shape,prism-like shape, cylindrical shape (annular shape), circular shape,plate-like shape, curved plate-like shape, and the like are acceptable.As to the dimensions, all sizes starting from large-sized one toultraminuaturized one are acceptable. However, as repeatedly describedin this specification, the present invention is particularlyadvantageous when it is used for miniaturized magnets andultraminiaturized magnets.

[0174] Further, in the present invention, it is preferred that thecoercive force (H_(CJ)) (coercive force at a room temperature) of thebonded magnet is 320 to 1200 kA/m, and 400 to 800 kA/m is morepreferable. If the coercive force (H_(JC)) is lower than the lower limitvalue, demagnetization occurs conspicuously when a reverse magneticfield is applied, and the heat resistance at a high temperature isdeteriorated. On the other hand, if the coercive force (H_(CJ)) exceedsthe above upper limit value, magnetizability is deteriorated. Therefore,by setting the coercive force (H_(CJ)) to the above range, in the casewhere the bonded magnet is subjected to multipolar magnetization, asatisfactory magnetization can be accomplished even when a sufficientlyhigh magnetizing field cannot be secured. Further, it is also possibleto obtain a sufficient magnetic flux density, thereby enabling toprovide high performance bonded magnets.

[0175] Furthermore, in the present invention, it is preferable that themaximum magnetic energy product (BH)_(max) of the bonded magnet is equalto or greater than 40 kJ/m³, more preferably equal to or greater than 50kJ/m³, and most preferably in the range of 70 to 120 kJ/m³. If themaximum magnetic energy product (BH)_(max) is less than 40 kJ/m³, it isnot possible to obtain a sufficient torque when used for motorsdepending on the types and structures thereof.

[0176] As described above, according to the cooling roll of thisembodiment of the present invention, since the ridges 55 acting as thedimple correcting means are provided on the cooling roll 5, dimples tobe formed on the roll contact surface 81 of the melt spun ribbon 8 areproduced in a divided state. Therefore, It Is possible to preventformation of huge dimples, so that dispersion or variation in thecooling rates becomes small. With this result, it is possible to obtaina melt spun ribbon having less dispersion in its crystal grain sizes andhaving stably high magnetic properties.

[0177] Therefore, bonded magnets manufactured from the obtained meltspun ribbons can also have high magnetic properties. Further, highmagnetic properties can be obtained without pursing high density whenmanufacturing the bonded magnets. This means that the obtained bondedmagnets can have improved moldability, dimensional accuracy, mechanicalstrength, corrosion resistance and heat resistance and the like.

[0178] Next, the second embodiment of the cooling roll 5 according tothe present invention will be described. In this regard, FIG. 13 is afront view which schematically shows the second embodiment of thecooling roll 5 according to the present invention, and FIG. 14 is asectional view which schematically shows the structure of a portion inthe vicinity of the circumferential surface of the cooling roll 5 shownin FIG. 13. Hereinbelow, a description will be made with regard to thecooling roll 5 of the second embodiment by focusing on different pointsbetween the first and second embodiments, and explanation for the commonpoints is omitted.

[0179] As shown in FIG. 13, the ridges 55 which act as the dimplecorrecting means are spirally formed with respect to the rotation axis50 of the cooling roll 5. The ridges 55 having such spiral forms can beformed relatively easily over the entire of the circumferential surface53. For example, the grooves 54 can be formed by cutting the outercircumferential portion of the cooling roll 5 with a cutting tool suchas a lathe which is moved in a constant speed in parallel with therotation axis 50 of the cooling roll 5 under the state that the coolingroll 5 is being rotated In a constant speed. With this result, theremaining portions of the circumferential surface 53 between theadjacent grooves 54 and 54 constitute the ridges 55.

[0180] In this regard, it is to be understood that the number of thespiral groove 54 (or ridge 55) may be one or more.

[0181] Further, the angle θ (absolute value) defined between thelongitudinal direction of the groove 54 (or ridge 55) and the rotationaldirection of the cooling roll 5 should preferably be equal to or lessthan 30°, and more preferably equal to or less than 20°. If the angle θis equal to or less than 30° the gas that has entered between thecircumferential surface 53 and the puddle 7 can be expelled efficientlyregardless of the peripheral velocity of the cooling roll 5.Consequently, division for dimples is more effectively achieved, so thatthe area of each dimple and the total area of the dimples can be madesmall further.

[0182] Further, the angle θ may be changed so as to have the same valueor different values depending on locations on the circumferentialsurface 53. Further, when the two or more grooves 54 (or ridges 55) areformed, the angle θ may be changed in each of the grooves 54 (or ridges55).

[0183] In this embodiment, the ends of each groove 54 are formed intoopenings 57 opened at the opposite edge portions 56 of thecircumferential surface 53 in the end surfaces of the cooling roll 5,respectively. This arrangement makes it possible to discharge the gaswhich has been expelled from between the circumferential surface 53 andthe puddle 7 to the lateral sides of the cooling roll 5 through theopenings 57, so that it is possible to effectively prevent thedischarged gas from reentering between the circumferential surface 53and the puddle 7 again, thereby further improving the dimple correctingeffect. Although in the above example the groove 54 has the openings 56at the opposite ends thereof, such an opening may be provided at one ofthe ends thereof.

[0184] Next, the third embodiment of the cooling roll 5 according to thepresent invention will be described. In this regard, FIG. 15 is a frontview which schematically shows the third embodiment of the cooling roll5 according to the present invention, and FIG. 16 is a sectional viewwhich schematically shows the structure of a portion in the vicinity ofthe circumferential surface of the cooling roll 5 shown in FIG. 15.Hereinbelow, a description will be made with regard to the cooling roll5 of the third embodiment by focusing on different points between thethird embodiment and the first and second embodiments, and explanationfor the common points is omitted.

[0185] As shown in FIG. 15, in the circumferential surface 53, there areformed at least two spiral grooves 54 of which spiral directions aredifferent from each other so that these grooves 54 intersect to eachother at many locations.

[0186] In the same manner as the second embodiment described above, inthis embodiment the portions remaining in the circumferential surface 53between the adjacent grooves 54 and 54 constitute the ridges 55.

[0187] In this embodiment, by forming such grooves that are spiraled inthe opposite directions, the melt spun ribbon 8 receives laterallyexerted force from the dextral spirals as well as laterally exertedforce from the sinistral spirals and these forces are cancelled witheach other. Therefore, the lateral movement of the melt spun ribbon 8 1nFIG. 15 is suppressed so that the advancing direction of the melt spunribbon 8 becomes stable.

[0188] Further, it is preferred that the angles (absolute value) definedbetween each of the longitudinal directions of the grooves 54 and therotational direction of the cooling roll 5 (which are represented by θ₁and θ₂ in FIG. 15) are in the same range as that of the angle θdescribed above with reference to the second embodiment.

[0189] Next the fourth embodiment of the cooling roll 5 according to thepresent invention will be described. In this regard, FIG. 17 is a frontview which schematically shows the fourth embodiment of the cooling roll5 according to the present invention, and FIG. 18 is a sectional viewwhich schematically shows the structure of a portion in the vicinity ofthe circumferential surface of the cooling roll 5 shown in FIG. 17.Hereinbelow, as is the same manner with the second and thirdembodiments, a description will be made with regard to the cooling roll5 of the fourth embodiment by focusing on different points between thefourth embodiment and the first, second and third embodiments, andexplanation for the common points is omitted.

[0190] As shown in FIG. 17, in this embodiment, the cooling roll 5 isformed with a plurality of V-shaped grooves each having a peak at thecenter of the width of the circumferential surface 53 of the coolingroll 5 along the axial direction thereof and two extending groovesextending to the edges 56 of the circumferential surface 53.

[0191] In this embodiment, by forming the grooves 54 having the aboveshape, the portions remaining in the circumferential surface 53 otherthan the grooves 54 and 54 constitute the ridges 55 comprised of aplurality of V-shape ridges.

[0192] When the cooling roll 5 having these grooves 54 are used, it ispossible to expel the gas entered between the circumferential surface 53and the puddle 7 more effectively by appropriately arranging suchgrooves with respect to the rotational direction of the cooling roll 5.Consequently, division for dimples is more effectively achieved, so thatthe area of each dimple and the total area of the dimples can be madesmall further.

[0193] Further, when the cooling roll 5 having these grooves 54 areused, the melt spun ribbon 8 receives laterally exerted force from thegrooves 54 located at one side thereof as well as laterally exertedforce from the grooves 54 located at the other side thereof and theseforces are balanced with each other (see FIG. 17). As a result, the meltspun ribbon 8 is positioned at the center of the cooling roll 5 in theaxial direction thereof so that the advancing direction of the melt spunribbon 8 becomes stable.

[0194] Although the dimple correcting means of the present invention wasdescribed above with reference to the first to fourth embodiments, thestructure of the dimple correcting means such as its shape or form isnot limited to those of the embodiments.

[0195] For example, although in the above embodiments the ridges actingas the dimple correcting means are constructed from the remaining shapeof the circumferential surface that can be obtained as a result of theformation of the grooves, the ridges may be formed by using othermethods. For example, the ridges may be formed by providing othermembers formed of the same material as the surface layer onto thecircumferential surface of the cooling roll.

[0196] Further, it is to be understood that the shape or form of thedimple correcting means is not limited to the ridge mentioned above, andvarious shapes or forms can be used if they can exhibit the function forcorrecting dimples to formed on the roll contact surface of the meltspun ribbon.

[0197] For example, as shown in FIG. 19, the dimple correcting means ofthe present invention can be formed from a number of separate shortslanting grooves 54. Further, the cross sectional shape of each groove54 may be formed into one shown in FIG. 20 or FIG. 21.

[0198] According to the cooling rolls 5 shown in FIGS. 19 to 21, it isalso possible to obtain the same results as those of the first to fourthembodiments.

EXAMPLES

[0199] Hereinafter, actual examples of the present invention will bedescribed.

Example 1

[0200] A cooling roll having the dimple correcting means shown in FIGS.1 to 3 was manufactured, and then a melt spinning apparatus equippedwith the cooling roll shown in FIG. 1 was prepared.

[0201] The cooling roll was manufactured as follows.

[0202] First, a roll base (having diameter of 200 mm and width of 30 mm)made of a copper (having heat conductive of 395 W·m^(−1·)K⁻¹ at t atemperature of 20° C. and coefficient of thermal expansion of16.5×10⁻⁶K⁻¹ at a temperature of 20° C.) was prepared, and then it wasground so as to have a mirror finishing outer circumferential surfacewith a surface roughness Ra of 0.07 μm.

[0203] Then, a plurality of grooves 54 which extend in parallel with therotational direction of the roll base were formed by cutting.

[0204] As a result of the formation of the grooves 54, ridges 55 thatare the remaining portions between the adjacent grooves 54 are formedwith the circumferential surface 53 of the cooling roll 5.

[0205] Next, a surface layer of ZrC (a kind of ceramics) (having heatconductivity of 20.6 W·m⁻¹K⁻¹ at a temperature of 20° C. and coefficientof thermal expansion of 7.0×10⁶K⁻¹ at a temperature of 20° C.) wasformed onto the outer circumferential surface of the roll base by meansof ion plating to obtain the cooling roll shown in FIGS. 1 to 3.

[0206] By using the melt spinning apparatus 1 having thus obtainedcooling roll 5, melt spun ribbons made of an alloy compositionrepresented by the formula of(Nd_(0.75)Pr_(0.20)Dy_(0.05))_(9.0)Fe_(hal) Co_(8.2)B_(5.6) weremanufactured in accordance with the following method.

[0207] First, an amount (basic weight) of each of the materials Nd, Pr,Dy, Fe, Co and B was measured, and then a mother alloy ingot wasmanufactured by casting these materials.

[0208] Next, the mother alloy ingot was put into a crystal tube of themelt spinning apparatus 1 having a nozzle (circular orifice) 3 at thebottom thereof. There after, a chamber in which the melt spinningapparatus 1 is installed was vacuumed, and then an inert gas (Heliumgas) was introduced to create a desired atmosphere of predeterminedtemperature and pressure.

[0209] Next, the mother alloy ingot in the crystal tube was melt byheating it by means of high frequency inductive heating. Then, under theconditions that the peripheral velocity of the cooling roll 5 was set tobe 28 m/sec, the injection pressure (that is, the differential pressurebetween the ambient pressure and the summed pressure of the internalpressure of the crystal tube and the pressure applied to the surface ofthe liquid in the tube which is in proportion to the liquid level) ofthe molten alloy 6 was set to be 40 kPa, and the pressure of the ambientgas was set to be 60 kPa, the molten alloy 6 was injected toward theapex of the cooling roll 5 from just above the rotational axis of thecooling roll 5, to manufacture a melt spun ribbon 8 continuously.

Examples 2 to 7

[0210] In addition to the above, another six types of cooling rolls eachhaving the same configuration as that of the cooling roll of Example 1excepting that the shape and form of the grooves were formed into thoseshown in FIGS. 13 and 14 were manufactured. Here, it should be notedthat these cooling rolls were manufactured so that the average width ofeach groove, the average width of each ridge, the average depth of eachgroove (the average height of each ridge), the average pitch of theadjacent grooves (ridges) were different from with each other in each ofthe cooling rolls. Further, in each of the cooling rolls, three grooveswere formed using a lathe having three cutting tools arranged so as tohave the same interval so that the adjacent grooves have substantiallythe same pitch in all the portions in the circumferential surfacesthereof. Further, in each of these cooling rolls, the angle θ definedbetween the longitudinal direction of each groove and the rotationaldirection the cooling roll was set to be 5°. Thereafter, by replacingthe cooling roll of the melt spinning apparatus used in Example 1 witheach of these cooling rolls sequentially, melt spun ribbons weremanufactured in the same manner as Example 1.

Example 8

[0211] Further, another cooling roll was also manufactured in the samemanner as the cooling roll of Example 2 excepting that the shape andform of the grooves and ridges were formed into those shown in FIGS. 15and 16. Thereafter, in the same manner as Example 1, a melt spun ribbonwas manufactured by replacing the cooling roll of the melt spinningapparatus with this cooling roll. In this regard, it is to be noted thatin this Example 8 the angle θ₁ and θ₂ each defined between thelongitudinal direction of each groove and the rotational direction thecooling roll was set to be 15°

Example 9

[0212] Furthermore, another cooling roll was also manufactured in thesame manner as the cooling roll of Example 1 excepting that the shapeand form of the grooves and ridges were formed into those shown in FIGS.17 and 18. Thereafter, in the same manner as Example 1, a melt spunribbon was manufactured by replacing the cooling roll of the meltspinning apparatus with this cooling roll. In this regard, it is to benoted that in this Example 9 the angle θ₁ and θ₂ each defined betweenthe longitudinal direction of each groove and the rotational directionthe cooling roll was set to be 20°.

Comparative Example

[0213] Moreover, another cooling roll was also manufactured in the samemanner as the cooling roll of Example 1 excepting that no grooves orridges were formed after the outer circumferential surface had beenformed into a mirror finishing surface by grinding. Then, in the samemanner as Example 1, a melt spun ribbon was manufactured by replacingthe cooling roll of the melt spinning apparatus with this cooling roll.

[0214] In each of these cooling rolls of the Examples 1 to 9 andComparative Example, the thickness of each surface layer was 7 μm.Further, in each of the cooing rolls, no machine work was carried outonto the surface layer after the formation of the surface layers.

[0215] In each of these cooling rolls mentioned above, the width of eachgroove L₁ (average value), the width of each ridge L₂ (average value),the depth of each groove (the height of each ridge) L₃ (average value),the pitch L₄ (average value) of the adjacent grooves (ridges), and theratio of the projected area of the grooves with respect to the projectedarea of a predetermined portion of the circumferential surface of thecooling roll were measured, and the measured values thereof are shown inthe attached TABLE 1.

[0216] Next, the surface structure (condition) of the roll contactsurface of each of the melt spun ribbons of Examples 1-9 and ComparativeExample was observed using a scanning electronic-microscope (SEM). As aresult, it was confirmed that in all the melt spun ribbons of Examples1-9, ridges and grooves corresponding to the grooves and ridges of thecircumferential surfaces of the cooling rolls were formed on their rollcontact surfaces due to transfer of the shapes of the circumferentialsurfaces of the cooling rolls, so that dimples were produced on theirroll contact surfaces with a stated that they were divided by the ridgesor grooves. On the other hand, in the melt spun ribbon of ComparativeExample, it was confirmed that many huge dimples were produced on theroll contact surface thereof. In this connection, FIG. 22 shows anelectronic micrograph of the roll contact surface of the melt spunribbon of Example 3.

[0217] In addition, the following evaluations (1) and (2) were made foreach of the melt spun ribbons of Examples 1 to 9 and ComparativeExample.

[0218] (1) Magnetic Properties of the Respective Melt Spun Ribbons

[0219] A strip of the melt spun ribbon having the length of 5 cm was cutout from each of the melt spun ribbons, and then five samples eachhaving the length of about 7 mm were obtained from each strip.Thereafter, for each of the samples, the average thickness t, the ratioof the projected area of the huge dimples (having an area equal to orgreater than 2000 μm²) produced on the roll contact surface thereof, theratio of the projected area (total area) of all the dimples produced onthe roll contact surface thereof, and the magnetic properties thereofwere measured.

[0220] The thickness was measured using a micrometer at 20 samplingpoints in each of the samples, and the average of the measured valueswas used as the average thickness t. The ratio of the projected area ofthe huge dimples (having an area equal to or greater than 2000 μm²)produced on the roll contact surface and the ratio of the projected area(total area) of all the dimples produced on the roll contact surfacewere obtained from the observation results by the scanning electronicmicroscope (SEM). With regard to the magnetic properties, the coerciveforce H_(CJ) (kA/m) and the maximum energy product (BH)_(max) (kJ/m³)were measured using a vibration type sample magnetometer (VSM). In themeasurement, the magnetic field was applied along the major axis of therespective melt spun ribbons. However, no demagnetization correction wasperformed.

[0221] (2) Magnetic Properties of Bonded Magnets

[0222] Each of the melt spun ribbons was subjected to a heat treatmentin the argon gas atmosphere at a temperature of 675° C. for 300 sec.

[0223] Each of the melt spun ribbons to which the heat treatment hadbeen made was them milled to obtain a magnetic powder of the meanparticle size (diameter) of 75 μm.

[0224] To analyze the phase structure of the obtained magnetic powders,the respective magnetic powders were subjected to an X-ray diffractiontest using Cu-Kα line at the diffraction angle (2θ) of 20°-60°. Withthis result, from the diffraction pattern of the respective magneticpowders, it was confirmed that in each of the magnetic powders therewere a diffraction peak of a hard magnetic phase of R₂ (Fe, Co)₁₄Bphase, and a diffraction peak of a soft magnetic phase of α-(Fe, Co)phase. Further, from the observation results by the transmissionelectron microscope (TEM), the respective magnetic powders had acomposite structure (nanocomposite structure). Furthermore, in each ofthe magnetic powders, an average grain size of each of these phases wasalso measured.

[0225] Next, each of the magnetic powders was mixed with an epoxy resinto obtain compositions for bonded magnets (compounds). In this case,each compound had the same mixing ratio (parts by weight) of themagnetic powder and the epoxy resin. Namely, in each sample, about 97.5wt % of magnetic powder was contained.

[0226] Thereafter, each of the thus obtained compounds was milled orcrushed to be granular. Then, the granular substance (particle) wasweighed and filled into a die of a press machine, and then it wassubjected to a compaction molding (in the absence of a magnetic field)at a temperature of 12 ° C. and under the pressure of 600 MPa, to obtaina mold body. The mold body was then removed from the die, and it washardened by heating at a temperature of 175° C. to obtain a bondedmagnet of a columnar shape having a diameter of 10 mm and a height of 8mm.

[0227] Next, after pulse magnetization was performed for the respectivebonded magnets under the magnetic field strength of 3.2 MA/m, magneticproperties (remanent magnetic flux density Br, coercive force H_(CJ),and maximum magnetic energy product (BH)_(max)) were measured using a DCrecording fluxmeter (manufactured and sold by Toei Industry Co. Ltd withthe product code of TRF-5BH) under the maximum applied magnetic field of2.0 MA/m. The temperature at the measurement was 23° C. (that is, roomtemperature).

[0228] The results of the measurements are shown in the attached TABLES2 to 4.

[0229] As seen from the attached Tables 2 and 3, in each of the meltspun ribbons of Examples 1 to 9, the ratio of the area occupied by thehuge dimples is relatively small so as to lie within the range of 0.1 to3.8%, and the ratio of the area (total area) occupied by the dimples isalso small. Further, these melt spun ribbons have less dispersion intheir magnetic properties, and they have generally excellent magneticproperties. This is supposed to result from the following reasons.

[0230] Namely, the cooling rolls of Examples 1 to 9 have the dimplecorrecting means on their circumferential surfaces. Therefore,production of huge dimples on their roll contact surfaces are preventedor suppressed. Therefore, if dimples are produced on the roll surfaces,an area (size) of each dimple is relatively small, and therefore thetotal area occupied by the produced dimples also becomes small.Consequently, the difference in cooling rates at various portions ofeach puddle also becomes small, so that it is possible to obtain a meltspun ribbon having less dispersion in its crystal grain sizes andmagnetic properties.

[0231] On the other hand, in the melt spun ribbon of ComparativeExample, the ratio of the area occupied by the huge dimples isrelatively large so at to lie within the range of 15.5-25.5%, and theratio of the area (total area) occupied by the dimples is also large incomparison with the melt spun ribbons of the present invention. Further,there is large dispersion in its magnetic properties in spite of thefact that it has been cut out from the same melt spun ribbon. This issupposed to result from the following reasons.

[0232] In the melt spun ribbon of Comparative Example, many huge dimpleswere produced on the roll contact surface of the melt spun ribbon due tothe gas which had entered between the puddle and the circumferentialsurface. Due to the formation of such huge dimples, the cooling rate atthe portions of the roll contact surface (in particular, at the portionsaround the centers of the respective huge dimples) that did not contactwith the circumferential surface of the cooling roll was lowered whilethe cooling rate at the portions of the roll contact surface that werein contact with the circumferential surface was relatively large, andsuch difference In the cooling rates produced coarse of the crystalgrain size. It is believed that this difference in the cooling ratesalso caused the large dispersion in the magnetic properties of theobtained melt spun ribbon.

[0233] Further, as apparent from the attached Table 4, the bondedmagnets formed from the melt spun ribbons of Examples 1 to 9 haveexcellent magnetic properties, while the bonded magnet formed fromComparative Example has merely poor magnetic properties.

[0234] This is supposed to result from the following reasons. Namely,the bonded magnets of Examples 1 to 9 are formed from the magneticpowders obtained from the melt spun ribbons having excellent magneticproperties and less dispersion in their magnetic properties, while thebonded magnet of Comparative Example is formed from the magnetic powderobtained from the melt spun ribbon having large dispersion in itsmagnetic properties, so that it is believed that the bonded magnet ofComparative Example has poor magnetic properties as a whole.

[0235] As described above, according to the present invention, thefollowing effects are realized.

[0236] Since the dimple correcting means is provided on thecircumferential surface of the cooling roll, formation of huge dimpleson the roll contact surfaced of the melt spun ribbon is prevented orsuppressed. Further, even if dimples are produced on the roll surfaces,an area (size) of each dimple is relatively small, and therefore thetotal area occupied by the produced dimples also becomes small.Consequently, the difference in cooling rates at various portions ofeach puddle also becomes small, so that it is possible to stably obtaina melt spun ribbon having excellent magnetic properties.

[0237] In particular, by appropriately selecting the structural materialand thickness of the surface layer and setting the shape and form of thegrooves and ridges acting as the dimple correcting means, it is possibleto control the area (size) of each dimple produced on the roll contactsurface of the melt spun ribbon and the total area of the produceddimples properly, thereby enabling to obtain a magnetic material havingexcellent magnetic properties.

[0238] Further, since the magnetic powder is constituted from acomposite structure having a soft magnetic phase and a hard magneticphase, the magnetic powder can have high magnetizability and exhibitexcellent magnetic properties, and in particular coercive force and heatresistance are enhanced.

[0239] Furthermore, since high magnetic flux density can be obtained, itis possible to manufacture bonded magnets having high magneticproperties even if they are isotropic bonded magnets. In particular,according to the present invention, more excellent magnetic performancecan be obtained with a smaller size bonded magnet as compared with theconventional bonded magnet, it is possible to manufacture highperformance smaller size motors.

[0240] Moreover, since a higher magnetic flux density can be secured asdescribed above, in manufacturing bonded magnets sufficiently highmagnetic properties can be obtained without pursuing any means forelevating the density of the bonded magnet. As a result, the dimensionalaccuracy, mechanical strength, corrosion resistance, heat resistance(heat stability) and the like can be further improved in addition to theimprovement in the moldability, so that it is possible to readilymanufacture bonded magnets with high reliability.

[0241] Moreover, since the magnetizability of the bonded magnetaccording to this invention is excellent, it is possible to magnetize amagnet with a lower magnetizing field. In particular. multipolarmagnetization or the like can be accomplished easily and reliably, andfurther a high magnetic flux density can be also obtained.

[0242] Since a high density is not required to the bonded magnet, thepresent invention can be adapted to the manufacturing method such as theextrusion molding method or the injection molding method by whichmolding at high density is difficult as compared with the compactionmolding method, and the effects described in the above can also berealized in the bonded magnet manufactured by these molding methods.Accordingly, various molding methods can be selectively used and therebythe degree of selection of shape for the bonded magnet can be expanded.

[0243] Finally, it is to be understood that the present invention is notlimited to the embodiments and examples described above, and manychanges or additions may be made without departing from the scope of theinvention which is determined by the following claims. TABLE 1Conditions of Circumferential Surfaces of Cooling Rolls, Grooves andRidges Average Width Average Width Average Depth Average Ratio ofProjected of Groove L₁ (μm) of Ridge L₂ (μm) of Groove L₃ (μm) Pitch L₄(μm) Area of Grooves (%) Example 1 22.5 2.5 3.5 25.0 90 Example 2 20.040.0 3.0 40.0 50 Example 3 10.0 12.0 1.5 12.0 83 Example 4 27.0 90.0 8.090.0 30 Example 5 30.0 50.0 2.0 50.0 60 Example 6 28.0 68.0 5.3 68.0 41Example 7 5.0 7.5 1.0 7.5 67 Example 8 9.5 15.0 2.5 15.0 63 Example 920.0 30.0 1.5 30.0 67 Comp.Ex. — — — — —

[0244] TABLE 2 Properties of Melt Spun Ribbons (Example 1 to 5) AverageRatio of Projected Area Ratio of Total Thickness of Huge Dimples Area ofDimples H_(CJ) Br (BH)_(max) Sample No. (μm) (%) (%) (kA/m) (T) (kJ/m³)Example 1 1 19 1.9 20 562 1.05 155 2 19 1.5 18 564 1.04 154 3 20 2.2 23566 1.02 150 4 20 1.6 19 561 1.03 152 5 20 2.1 22 559 1.03 153 Example 21 20 2.3 26 548 1.02 149 2 21 2.0 20 554 1.02 150 3 22 2.2 23 546 1.00145 4 21 2.5 27 549 1.01 147 5 21 2.2 22 550 1.01 148 Example 3 1 19 0.219 561 1.05 155 2 18 0.1 12 570 1.06 162 3 19 0.2 18 562 1.05 156 4 190.2 16 563 1.05 158 5 18 0.1 14 568 1.06 160 Example 4 1 19 3.5 31 5380.99 144 2 20 3.8 34 553 0.98 142 3 25 3.6 32 542 0.96 140 4 24 3.7 35540 0.96 139 5 21 3.7 32 550 0.97 141 Example 5 1 19 2.2 25 558 1.03 1522 22 2.1 23 552 1.02 151 3 20 1.7 19 563 1.05 156 4 21 1.9 20 560 1.04154 5 20 2.0 21 558 1.04 153

[0245] TABLE 3 Properties of Melt Spun Ribbons (Example 6 to 9, Comp.Ex.) Average Ratio of Projected Area Ratio of Total Thickness of HugeDimples Area of Dimples H_(CJ) Br (BH)_(max) Sample No. (μm) (%) (%)(kA/m) (T) (kJ/m³) Example 6 1 23 2.1 25 557 1.01 148 2 22 1.7 20 5551.03 151 3 21 2.0 23 554 1.02 149 4 22 1.5 24 552 1.02 150 5 23 1.8 22548 1.01 147 Example 7 1 18 0.3 13 570 1.08 160 2 19 0.5 20 569 1.06 1593 18 0.2 11 572 1.07 162 4 20 0.3 15 564 1.04 157 5 19 0.4 18 567 1.05158 Example 8 1 21 0.8 18 552 1.04 153 2 20 0.7 17 556 1.03 152 3 19 0.916 582 1.05 156 4 21 1.2 21 555 1.03 151 5 19 1.0 19 580 1.04 154Example 9 1 22 2.3 28 557 1.01 148 2 20 2.0 24 562 1.02 150 3 21 1.8 20560 1.01 149 4 21 2.1 25 559 1.03 152 5 19 1.9 23 564 1.02 151 Comp.Ex.1 19 15.5 43 330 0.81 73 2 32 18.0 48 280 0.67 57 3 20 22.3 53 303 0.7769 4 25 19.0 49 319 0.79 70 5 17 25.5 58 295 0.75 60

[0246] TABLE 4 Mean Crystal Grain Sizes of Magnetic Powders and MagneticProperties of Bonded Magnets Mean Crystal Grain Size H_(CJ) Br(BH)_(max) (nm) (kA/m) (T) (kJ/m³) Example 1 29 562 0.87 110 Example 235 550 0.84 103 Example 3 25 565 0.89 117 Example 4 40 543 0.82  98Example 5 30 560 0.87 108 Example 6 34 553 0.84 104 Example 7 27 5680.88 116 Example 8 32 558 0.86 107 Example 9 33 561 0.86 105 Comp.Ex. 67300 0.68  49

What is claimed is:
 1. A cooling roll for manufacturing a ribbon-shapedmagnetic material by colliding a molten alloy to a circumferentialsurface of the cooling roll so as to cool and then solidify it, whereinthe circumferential surface of the cooling roll has dimple correctingmeans for dividing dimples to be produced on a roll contact surface ofthe ribbon-shaped magnetic material which is in contact with thecircumferential surface of the cooling roll.
 2. The cooling roll asclaimed in claim 1, wherein the cooling roll includes a roll base and anouter surface layer provided on an outer peripheral portion of the rollbase, and the outer surface layer has said dimple correcting means. 3.The cooling roll as claimed in claim 2, wherein the outer surface layerof the cooling roll is formed of a material having a heat conductivitylower than the heat conductivity of the structural material of the rollbase at or around room temperature.
 4. The cooling roll as claimed inclaim 2, wherein the outer surface layer of the cooling roll is formedof a ceramic.
 5. The cooling roll as claimed in claim 2, wherein theouter surface layer of the cooling roll is formed of a material having aheat conductivity equal to or less than 80 Wm⁻¹K⁻¹ at or around roomtemperature.
 6. The cooling roll as claimed in claim 2, wherein theother surface layer of the cooling roll is formed of a material having acoefficient of thermal expansion in a range of 3.5−18[×10⁻⁶K⁻¹] at oraround room temperature.
 7. The cooling roll as claimed in claim 2,wherein the average thickness of the outer surface layer of the coolingroll is 0.5 to 50 m.
 8. The cooling roll as claimed in claim 2, whereinthe outer surface layer of the cooling roll is manufactured withoutexperiencing a machining process.
 9. The cooling roll as claimed inclaim 1, wherein the dimple correcting means includes at least one ridgeprovided on the circumferential surface of the cooling roll.
 10. Thecooling roll as claimed in claim 9, wherein an average width of theridge is 0.5-95 μm.
 11. The cooling roll as claimed in claim 9, whereinthe at least one ridge is provided by forming at least one groove in thecircumferential surface of the cooling roll.
 12. The cooling roll asclaimed in claim 11, wherein an average width of the groove is 0.5-90μm.
 13. The cooling roll as claimed in claim 11, wherein an averageheight of the ridge or an average depth of the groove is 0.5-20 μm. 14.The cooling roll as claimed in claim 11, wherein the ridge or groove isformed spirally with respect to the rotation axis of the cooling roll.15. The cooling roll as claimed in claim 11, wherein the at least oneridge or groove includes a plurality of ridges or grooves which arearranged in parallel with each other through an average pitch of 0.5-100μm.
 16. The cooling roll as claimed in claim 9, wherein a ratio of aprojected area of the ridge or groove with respect to a projected areaof the circumferential surface is equal to or greater than 10%.
 17. Aribbon-shaped magnetic material which is manufactured by colliding amolten alloy to a circumferential surface of a cooling roll so as tocool and then solidify it, wherein the circumferential surface of thecooling roll has dimple correcting means for dividing dimples to beproduced on a roll contact surface of the ribbon-shaped magneticmaterial which is in contact with the circumferential surface of thecooling roll.
 18. The ribbon-shaped magnetic material as claimed inclaim 17 wherein grooves or ridges are formed in the roll contactsurface so that produced dimples are divided by the grooves or ridges.19. The ribbon-shaped magnetic material as claimed in claim 17, whereinthe dimples produced on the roll contact surface of the ribbon-shapedmagnetic material upon solidification thereof include huge dimples eachhaving an area equal to or greater than 2000 μm², in which the ratio ofan area in the roll contact surface occupied by thus produced hugedimples with respect to a total area of the roll contact surface of theribbon-shaped magnetic material is equal to or less than 10%.
 20. Theribbon-shaped magnetic material as claimed in claim 17, wherein thedivision of the dimples to be produced is carried out by transferring ashape of at least a part of the circumferential surface of the coolingroll to the roll contact surface of the ribbon-shaped magnetic material.21. The ribbon-shaped magnetic material as claimed in claim 16, whereinan average thickness of the ribbon-shaped magnetic material is 8-50 μm.22. A magnetic powder which is obtained by milling a ribbon-shapedmagnetic material which is manufacturing by colliding a molten alloy toa circumferential surface of a cooling roll so as to a cool and thensolidify it, wherein the circumferential surface of the cooling roll hasdimple correcting means for dividing dimples to be produced on a rollcontact surface of the ribbon-shaped magnetic material which is incontact with the circumferential surface of the cooling roll.
 23. Themagnetic powder as claimed in claim 22, wherein the magnetic powder issubjected to at least one heat treatment during or after a manufacturingprocess thereof.
 24. The magnetic powder as claimed in claim 22, whereina mean particle size of the magnetic powder is 1-300 μm.
 25. Themagnetic powder as claimed in claim 22, wherein the magnetic powder hasa composite structure composed of a hard magnetic phase and a softmagnetic phase.
 26. The magnetic powder as claimed in claim 25, whereinan average crystal grain size of each of the hard magnetic phase and thesoft magnetic phase is 1-100 nm.
 27. A bonded magnet which ismanufactured by binding a magnetic powder which is obtained by milling aribbon-shaped magnetic material which is manufactured by colliding amolten alloy to a circumferential surface of a cooling roll so as tocool and then solidify it, wherein the circumferential surface of thecooling roll has dimple correcting means for dividing dimples to beproduced on a roll contact surface of the ribbon-shaped magneticmaterial which is in contact with the circumferential surface of thecooling roll.
 28. The bonded magnet as claimed in claim 27, wherein anintrinsic coercive force (H_(CJ)) of the bonded magnet at roomtemperature lies within a range of 320-1200 kA/m.
 29. The bonded magnetas claimed in claim 27, wherein a maximum magnetic energy product(BH)_(max) of the bonded magnet is equal to or greater than 40 kJ/m³.